Sold as Talin®
Thaumatin is a protein which is isolated from the katemfe fruit, Thaumatococcus daniellii Benth, also called "the miraculous fruit of the Sudan." Katemfe is common in the West African rain forest zone. The fruit contains 1-3 black seeds surrounded by a gel, and capped with a membranous sac, the aril, which contains the sweet material. This is used as a sweetener in cooking, in flavoring palm wine, and in making confections for children.
Thaumatin is sweet, with a slow onset, lingering sweetness and a licorice after-taste. Sweetness potency relative to sucrose is about 2000 x on a weight basis.
Thaumatin is a protein, so it has 4 calories per gram. Since it has such high potency relative to sucrose, the amount used is extremely small, and so it does not provide measurable caloric value at use levels in foods.
Thaumatin is very water-soluble and heat-stable.
In the United States, thaumatin has GRAS status as a flavor enhancer; it does not have approval as a sweetener. JECFA and EFSA consider thaumatin safe for use as a sweetener.
Thaumatin is digested like any other protein, so there is no concern about toxicity. Thaumatin is reported to be allergenic, but less so than house dust mites.
Due to its slow onset and licorice-like off taste, thaumatin is unlikely to be used as a sole sweetener in foods or beverages.